Abstract: The goal of this proposal is to uncover the molecular mechanisms by which the Fbw7 tumor suppressor is implicated in cellular senescence. The long-term goals of my career are to apply the insight of molecular and cellular biology to understand the physiological significance of protein degradation machinery that is important in the development of human malignancies and aging-associated disorders. Fbw7 is a substrate recognition subunit of the E3 ubiquitin ligase complex SCFFbw7, which is well known to target numerous cell cycle positive regulators for proteasome-dependent degradation. Recent intensive studies elucidated a crucial tumor suppressor function for Fbw7. However, the molecular mechanism by which Fbw7 is implicated in cellular senescence is currently unknown. Our preliminary data showed that Fbw7 negatively regulates the stability of Raptor and Rictor, the essential accessory proteins of the mTOR complexes (mTORC). The mTOR pathway plays a pivotal role in sensing nutrition and energy in cells. Interestingly, recent studies revealed that mTOR signaling also negatively regulates longevity across species (from yeasts to mice). However, the upstream regulatory pathways governing mTOR activity during the aging process remain largely unknown. We hypothesize that Fbw7 is an upstream negative regulator of the mTOR signaling pathway through which Fbw7 plays an important role in regulating cellular senescence. In this proposal, we plan to: 1) Determine the physiological significance of SCFFbw7 during senescence, 2) Determine the role of SCFFbw7 in modulating cellular senescence via regulation of Raptor and Rictor protein stability, 3) Determine whether regulation of Raptor and Rictor by Fbw7 has a physiological role in controlling aging in hematopoietic stem cells (HSCs). This K01 award will provide protected time for me to pursue the hypotheses of this proposal, obtain new skill sets to execute experiments and solve problems. In addition, the award will also allow me to focus my efforts on independently conducting basic and translational research, and training of future young scientists. Should I receive this award, I will pursue this research in Beth Israel Deaconess Medical Center (BIDMC) and Harvard Medical School, where authorities in the fields of PI3 kinase signaling and cellular senescence locate. The outcome of the proposed studies will help elucidate whether Fbw7 can directly regular aging in vivo, and whether loss of Fbw7 function causes cellular senescence of HSCs via up-regulation of the mTOR pathway, which may contribute to the pathogenesis of leukemia in the elderly population. Importantly, this study suggests that loss of Fbw7 could be a conceivable biomarker for age-related hematological disorders and hence sensitivity to the mTOR specific inhibitors. We expect this will provide evidence toward the rationale for using mTOR pharmacological intervention in personalized medicine for age-related diseases.